The process of impurity induced layer disordering (IILD) has been applied to the fabrication of a wide variety of device structures, primarily in the AlGaAs alloy system. The relative ease with which this process is used in this system is in large part due to the close lattice match between the two binary constituents, AlAs and GaAs. Lattice match is therefore maintained throughout the interdiffusion process. For a more complete description of IILD, its benefits and applications, and how to produce the desired structures by various known treatments, see the detailed descriptions given in two commonly-owned U.S. Pat. Nos. 4,871,690 and 4,830,983, the contents of which patents are hereby incorporated by reference. The '690 patent also describes the manufacture of laser structures from the resultant semiconductor material with the IILD regions. The '983 patent also describes in detail specific processing techniques to control diffusion profiles for systematic reproduction. Also incorporated herein by reference is commonly-owned U.S. Pat. No. 4,980,893, which describes in detail the fabrication of multi-emitter laser arrays useful for high speed raster output scanners (ROS) and laser printing applications from the IILD material. This patent also shows the importance of p-side up mounting, whose significance will become apparent from the description that follows below.
Reference is also made to the previously published paper "Planar Diffusion-Based Processes For The Fabrication of Integrated Optical And Electrical Components", SPIE. Vol. 1582 Integrated Optoelectronics for Communication and Processing, pages 194-205, Sept. 1991. This paper, whose contents are hereby incorporated by reference, explains at great length the benefits of IILD in the fabrication of buried layer devices such as heterostructure lasers, FETs, and heterojunction bipolor transistors. What characterizes this class of devices is a very thin active region bounded on both sides by much thicker material layer. In the case of the laser, the thin region is a narrow filament of laser active region material surrounded on all sides by a material of wider bandgap. Laser action results from population inversion induced in the active region by introduced carriers. The inversion enables light amplification by stimulated emission, which means that light must be waveguided by the very thin region. Waveguiding is accomplished by the surrounding higher bandgap material which also has a lower refractive index and thus acts as an optical waveguide which maintains light in overlap with the thin active region, thus providing for amplification of light within the waveguide. In the FET application, the buried thin active region acts as the FET channel. In the bipolar transistor, it is the thin buried base region of the device, the thinner the base, the higher the operating frequency. In the laser application the active thin layers are one or more thin quantum well (QW) layers as well as possible thin barrier layers.
The performance of such buried layer III-V devices is profoundly affected by the quality of the semiconductor material. Defects, which includes dislocations, in the thin active layer or bounding layers materially affect laser light emission, transistor gain and in general device functionality. Many such devices must be made substantially defect-free in order that they have useful applications. The combination of a buried layer III-V device made by IILD, it has been observed, has a tendency to produce undesired defects under many circumstances involving systems other than the AlGaAs system mentioned above.
In more complicated III-V alloy systems in which the lattice parameter depends much more strongly on the proportions of the binary constituents, the process of enhancing the constituent interdiffusion rate can result in substantial strain within the crystal, potentially leading to threading dislocation and misfit dislocation formation. This becomes particularly the case when lattice parameter matching is accomplished through gradients in both the column III and the column V lattice constituents, as is the case at a GaInP/GaAs interface. In such cases, lattice strain during interdiffusion across the interface is minimal only when the enhanced rates of interdiffusion on both the column III and column V sites are equal. This is difficult to control because the relative rates of interdiffusion are typically a function of the concentrations of various point defect species such as Va.sub.III or I.sub.III. These point defects typically affect diffusion on III-sites and V-sites in fundamentally different ways. However, such structures incorporating phosphorus (P), such as with an AlInP, InGaAsP, or InGaP layer are highly desirable components as a result of their bandgap properties, as it results in light-emitting lasers emitting in wavelength ranges unavailable with AlGaAs, especially in the visible or further into the infra-red. Emission in the visible range is specially important for applications such as ROS. See, for instance, the Ikeda et al paper, published in App. Phys. Lett., 47(10), Nov. 15, 1985, pp. 1027-1028, which describes the fabrication of a room-temperature CW short wavelength DH laser in GaInP/AlGaInP grown on a GaAs substrate, the contents of which paper are incorporated herein by reference.
It is noted that Schwarz et al, in a paper entitled "InGaAs/InP Superlattice Mixing Induced By Zn or Si Diffusion", Appl. Phys.Lett., Vol 53, No. 12, pages 1051-1053, 1988, observed that in the InGaAs/InP system, in the fabrication of a superlattice structure, a 3.1% lattice mismatch can be accommodated in the mixed superlattice with no observable defects in the examined superlattice layers provided that the individual layer thickness was maintained below about 6-7 nm. It will be understood, however, that this teaching applies to a superlattice structure, which is a succession of thin layers bounded by thin layers, except for the bottommost layer or substrate. The superlattice structure is not commonly used to make semiconductor laser or transistor devices, which require that one or more thin layers must be bounded on both sides by thick layers for proper and efficient device operation, and, moreover, that the thick bounding layers must also be free of defects for the devices to operate properly. The Schwarz et al paper provides no teachings of how to achieve the foregoing, nor does it provide a teaching for III-V systems other than the one system described in the paper. The InGaAs/InP system is not suitable for visible light-emitting laser diodes as that compositional system would emit in the far infared region.